This invention relates in general to driving units for work spindles, and in particular to a position adjustable drive unit having a driving motor with adjustable rotary speed for use particularly in connection with sewing machines; the unit includes a regulator or controlling subunit which is provided with generators for producing signals corresponding to the actual rotary speed value and to the desired rotary speed value of the driving electric motor as well as to the actual position and to the desired position of the work spindle.
The position controlling drive units of this type are known, for example, from the U.S. Pat. Nos. 3,487,438, 3,532,953, 3,761,790, and 4,011,490.
In the following description, the position adjusting drive unit according to this invention will be explained in connection with an industrial sewing machine. It will be understood, however, that this unit can be readily adapted for numerous other adaptations, for example, for driving machine tools, winding machines for electrical capacitors, and the like. In industrial sewing machines which are also counted among machine tools and related products of the machine industry, a continuous increase of electronic components in the adjustable power drive units can be observed in recent designs. This development, however, causes considerable problems for final users inasmuch as the maintenance and servicing of such machines is traditionally done by mechanics in training who, even if experienced in the field of mechanics, usually have no skill in the field of electronics. From this point of view, the easiness to service and repair the position adjustable drive units in such machines is of particular importance.